Nonvolatile memory device and method of manufacturing the same

ABSTRACT

Provided is a nonvolatile memory device including a phase-change memory configured with cross-point memory cells in which memory elements formed of a phase-change material and selection elements formed with a diode are combined. A memory cell is configured with a memory element formed of a phase-change material and a selection element formed with a diode having a stacked structure of a first polycrystalline silicon film, a second polycrystalline silicon film, and a third polycrystalline silicon film. The memory cells are arranged at intersection points of a plurality of first metal wirings extending along a first direction with a plurality of third metal wirings extending along a second direction orthogonal to the first direction. An interlayer film is formed between adjacent selection elements and between adjacent memory elements, and voids are formed in the interlayer film provided between the adjacent memory elements.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a division of application Ser. No. 12/434,633filed May 2, 2009. This application also claims priority from JapanesePatent Application No. JP 2008-202771 filed on Aug. 6, 2008, the contentof which is hereby incorporated by reference into this application.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a nonvolatile memory device and amethod of manufacturing the same. More particularly, the presentinvention relates to a technique effectively applied to a nonvolatilememory device comprising a phase-change memory that stores a resistancevalue determined by a phase change between a crystalline state and anamorphous state of a metal compound in a nonvolatile manner and iselectrically rewritable, and a manufacture of the nonvolatile memorydevice.

BACKGROUND OF THE INVENTION

Some nonvolatile storage/memory devices utilize a crystalline state andan amorphous state of a metal compound as storage/memory information anda tellurium compound is typically used as its storage/memory material.The principle thereof is that a difference between a reflectivity of thecrystalline state and a reflectivity of the amorphous state of the metalcompound is stored as information, which is widely used in opticalinformation storage/memory media such as DVD (Digital Versatile Disk).

In recent years, there has been proposed to use a metal compound for anelectric information storage/memory medium. The method of using a metalcompound for an electric information storage/memory medium is, unlikethe optical method described above in which a metal compound is used foran optical information storage/memory medium, an electric method ofdetecting a difference in an electric resistance between the crystallinestate and the amorphous state of the metal compound, that is adifference between a low resistance state of crystal and a highresistance state of amorphia on the basis of the amount of current or achange in voltage. For example, U.S. Pat. No. 6,750,469 (PatentDocument 1) discloses an electric information memory medium using ametal compound called phase-change memory or phase-change type memory.

A structure of a basic memory cell of the phase-change memory isconfigured such that a memory element (phase-change material) and aselection element are combined. The phase-change memory stores and holdsinformation by making the memory element into the crystalline state orthe amorphous state by Joule heat generated in the memory element byapplying a current from the selection element. The rewriting can beperformed such that, in the case of obtaining the amorphous state withan electrically high resistance, a high current is applied to set atemperature of the memory element to be higher than a melting point andthen rapidly cooling down the memory element. In the case of obtainingthe crystalline state with an electrically low resistance, the currentto be applied is restricted to set the temperature of the memory elementto be a crystallization temperature lower than the melting point.Generally, the resistance value of the memory element is changed by 2digits or 3 digits according to the phase change. Thus, the phase-changememory has a read signal to be largely different depending on whetherthe memory element is in the crystalline state or the amorphous stateand is thus easy to perform a sensing operation.

For example, U.S. Pat. No. 6,579,760 (Patent Document 2) discloses aphase-change memory having cross-point memory cells which can bemanufactured at a low cost.

SUMMARY OF THE INVENTION

The cross-point memory cell needs to use a diode as selection element inorder to prevent erroneous information from being written. As describedabove, a current is flowed from the diode as selection element to aphase-change material as memory element so that information in thememory cell is rewritten. This fact means that the phase-change materialbecomes higher in its temperature in order to change the crystallinestate while the diode also becomes higher in its temperature due to itsresistance.

However, when the diode is at a high temperature, an impurity profileinside the diode breaks, which causes a problem that the OFF currentrequired for appropriate reading can not be maintained or the diodeitself is thermally broken down. It is also possible to use a materialhaving a high thermal conductivity for a material of the diode not tomake the diode to be a high temperature, but in this case, there will becaused a problem that a high current is required to set the phase-changematerial at a high temperature or the required high temperature is notreached to make information rewriting difficult. Thus, an object of thecross-point memory cell is to develop a memory cell structure in whichthe diode is less likely to be at a high temperature at the time ofrewriting and the phase-change material is likely to at a hightemperature.

It is an object of the present invention to provide a technique capableof realizing a memory cell structure in which a diode is less likely tobecome a high temperature even when the phase-change material is set ata high temperature in a nonvolatile memory device comprising aphase-change memory configured by cross-point memory cells in which amemory element formed of a phase-change material and a selection elementformed of a diode are combined.

The above and other objects and novel characteristics of the presentinvention will be apparent from the description of the presentspecification and the accompanying drawings.

One typical aspects of the inventions disclosed in the presentapplication will be briefly described as follows.

An aspect is a nonvolatile memory device having a phase-change memorywhich includes cross-point memory cells configured with a plurality offirst metal wirings extending along a first direction, a plurality ofthird metal wirings extending along a second direction orthogonal to thefirst direction, and memory elements and selection elements atintersection points of the first metal wirings and the third metalwirings. The memory cell is configured with the selection elementprovided on the first metal wiring, the memory element provided on theselection element, a second metal wiring provided on the memory element,and the third metal wiring provided on the second metal wiring, whereinan interlayer film is formed between the adjacent selection elements andbetween the adjacent memory elements, and a void is formed in theinterlayer film provided between the adjacent memory elements.

In addition, an aspect is a nonvolatile memory device having aphase-change memory which includes cross-point memory cells configuredwith a plurality of first metal wirings extending along a firstdirection, a plurality of third metal wirings extending along a seconddirection orthogonal to the first direction, and memory elements andselection elements at intersection points of the first metal wirings andthe third metal wirings. The memory cell is configured with theselection element provided on the first metal wiring, the memory elementprovided on the selection element, a second metal wiring provided on thememory element, and the third metal wiring provided on the second metalwiring, wherein an interlayer film having a lower thermal conductivitythan the interlayer film provided between the adjacent selectionelements is provided between the adjacent memory elements.

In addition, an aspect is a method of manufacturing a nonvolatile memorydevice having a phase-change memory which includes cross-point memorycells configured with a plurality of first metal wirings extending alonga first direction, a plurality of third metal wirings extending along asecond direction orthogonal to the first direction, and memory elementsand selection elements at intersection points of the first metal wiringsand the third metal wirings. At first, a first metal film, a selectionelement material, a buffer layer, a phase-change material, and a secondmetal film are sequentially formed on a semiconductor substrate. Then,the second metal film, the phase-change material, the buffer layer, theselection element material, and the first metal film are sequentiallyetched along the first direction to be processed to make thephase-change material into a stripe shape having a width narrower than awidth of the buffer layer or the selection element material.Subsequently, with forming a void between the adjacent phase-changematerials, a first interlayer film is filled between adjacent stackedpatterns formed of the second metal film, the phase-change material, thebuffer layer, the selection element material, and the first metal film.Subsequently, a surface of the first interlayer film is polished toexpose an upper surface of the second metal film, and then a third metalfilm is formed on the semiconductor substrate. Further, the third metalfilm, the second metal film, the phase-change material, the bufferlayer, and the selection element material are sequentially etched alongthe second direction to be processed to make the phase-change materialinto a stripe shape having a width narrower than the width of the bufferlayer or the selection element material. Subsequently, with forming avoid between the adjacent phase-change materials, a second interlayerfilm is filled between adjacent stacked patterns formed of the thirdmetal film, the second metal film, the phase-change material, the bufferlayer, the selection element material, and the first metal film.

In addition, an aspect is a method of manufacturing a nonvolatile memorydevice having a phase-change memory which includes cross-point memorycells configured with a plurality of first metal wirings extending alonga first direction, a plurality of third metal wirings extending along asecond direction orthogonal to the first direction, and memory elementsand selection elements at intersection points of the first metal wiringsand the third metal wirings. At first, a first metal film, a selectionelement material, a buffer layer, a phase-change material, and a secondmetal film are sequentially formed on a semiconductor substrate. Then,the second metal film, the phase-change material, the buffer layer, theselection element material, and the first metal film are sequentiallyetched along the first direction to be processed to make thephase-change material into a stripe shape. Subsequently, after thesecond metal film and the phase-change material are processed to be thinalong the first direction, side surfaces of the second metal film andthe phase-change material are coated and a first interlayer film to fillbetween adjacent stacked patterns formed of the buffer layer, theselection element material, and at the same time the first metal film isformed. Subsequently, after the first interlayer film is etched back, aspace occurring due to a coatability of the first interlayer film isfilled with the second interlayer film having a lower thermalconductivity than the first interlayer film. Subsequently, after thesurface of the second interlayer film is polished to expose the uppersurface of the second metal film, the third metal film is formed on thesemiconductor substrate. Further, the third metal film, the second metalfilm, the phase-change material, the buffer layer, and the selectionelement material are sequentially etched along the second direction tobe processed into a stripe shape. Subsequently, after the second metalfilm and the phase-change material are processed to be thin along thesecond direction, side surfaces of the second metal film and thephase-change material are coated, and at the same time a thirdinterlayer film is formed to fill between the adjacent stacked patternsformed of the buffer layer, the selection element material, and thefirst metal film. Subsequently, after the third interlayer film isetched back, a space occurring due to a coatability of the thirdinterlayer film is filled with a fourth interlayer film having a lowerthermal conductivity than the third interlayer film.

In addition, an aspect is a method of manufacturing a nonvolatile memorydevice having a phase-change memory which includes cross-point memorycells configured with a plurality of first metal wirings extending alonga first direction, a plurality of third metal wirings extending along asecond direction orthogonal to the first direction, and memory elementsand selection elements at intersection points of the first metal wiringsand the third metal wirings. At first, a first metal film, a selectionelement material, a buffer layer, a phase-change material, and a secondmetal film are sequentially formed on a semiconductor substrate. Then,the second metal film, the phase-change material, the buffer layer, theselection element material, and the first metal film are sequentiallyetched along the first direction to be processed to make thephase-change material into a stripe shape. Subsequently, after thesecond metal film and the phase-change material are processed to be thinalong the first direction, a first interlayer film to fill betweenadjacent stacked patterns formed of the buffer layer, the selectionelement material, and at the same time the first metal film is formed.Subsequently, the first interlayer film is etched back to remove thefirst interlayer film between the adjacent stacked patterns of thesecond metal film and the phase-change material. Subsequently, after thesecond interlayer film having a lower thermal conductivity than thefirst interlayer film is filled between the adjacent stacked patterns ofthe second metal film and the phase-change material, a surface of thesecond interlayer film is polished to expose an upper surface of thesecond metal film, and a third metal film is formed on the semiconductorsubstrate. Further, the third metal film, the second metal film, thephase-change material, the buffer layer, and the selection elementmaterial are sequentially etched along the second direction to beprocessed into a stripe shape. Subsequently, after the second metal filmand the phase-change material are processed to be thin along the seconddirection, a third interlayer film is formed to fill between theadjacent stacked patterns of the third metal film, the second metalfilm, the phase-change material, the buffer layer, the selection elementmaterial and the first metal film. Subsequently, the third interlayerfilm is etched back to remove the third interlayer film between theadjacent stacked patterns of the second metal film and the phase-changematerial. Subsequently, a fourth interlayer film having a lower thermalconductivity than the third interlayer film is filled between theadjacent stacked patterns of the second metal film and the phase-changematerial.

In addition, an aspect is a method of manufacturing a nonvolatile memorydevice having a phase-change memory which includes cross-point memorycells configured with a plurality of first metal wirings extending alonga first direction, a plurality of third metal wirings extending along asecond direction orthogonal to the first direction, and memory elementsand selection elements at intersection points of the first metal wiringsand the third metal wirings. At first, after a first metal film, aselection element material, a buffer layer, a phase-change material, anda second metal film are sequentially formed on a semiconductorsubstrate, the second metal film, the phase-change material, the bufferlayer, the selection element material, and the first metal film aresequentially etched along the first direction to be processed into astripe shape. Subsequently, after the second metal film and thephase-change material are processed to be thin along the firstdirection, an upper side of the buffer layer is processed to make itswidth narrower than a width of the lower side of the buffer layer.Subsequently, side surfaces of the second metal film and thephase-change material are coated, and at the same time the firstinterlayer film is formed to fill between adjacent stacked patterns ofthe buffer layer, the selection element material, and the first metalfilm, and a space occurring due to a coatability of the first interlayerfilm is filled with the second interlayer film having a lower thermalconductivity than the first interlayer film. Subsequently, aftersurfaces of the first interlayer film and the second interlayer film arepolished to expose the upper surface of the second metal film, a thirdmetal film is formed on the semiconductor substrate. Further, the thirdmetal film, the second metal film, the phase-change material, the bufferlayer, and the selection element material are sequentially etched alongthe second direction to be processed into a stripe shape. Subsequently,after the second metal film and the phase-change material are processedto be thin along the second direction, the upper side of the bufferlayer is processed to make its width narrower than the width of a lowerside of the buffer layer. Subsequently, the side surfaces of the secondmetal film and the phase-change material are coated, and at the sametime a third interlayer film is formed to fill between the adjacentstacked patterns of the buffer layer, the selection element material,and the first metal film, and a space occurring due to a coatability ofthe third interlayer film is filled with a fourth interlayer film havinga lower thermal conductivity than the third interlayer film.

In addition, an aspect is a method of manufacturing a nonvolatile memorydevice having a phase-change memory which includes cross-point memorycells configured with a plurality of first metal wirings extending alonga first direction, a plurality of third metal wirings extending along asecond direction orthogonal to the first direction, and memory elementsand selection elements at intersection points of the first metal wiringsand the third metal wirings. At first, after a first metal film, aselection element material, and a first buffer layer are sequentiallyformed on a semiconductor substrate, the first buffer layer, theselection element material, and the first metal film are sequentiallyetched along the first direction to be processed into a stripe shape.Subsequently, a first interlayer film is formed on the semiconductorsubstrate to embed between adjacent stacked patterns consisting of thefirst buffer layer, the selection element material and the first metalfilm, the surface of the first interlayer film is polished and the uppersurface of the first buffer layer is exposed. Subsequently, the firstbuffer layer and the selection element material are sequentially etchedalong the second direction to be processed into a stripe shape.Subsequently, after the second interlayer film is formed on thesemiconductor material to fill between the adjacent stacked patterns ofthe first buffer layer, the selection element material, and the firstmetal film, a surface of the second interlayer film is polished toexpose the upper surface of the first buffer layer. Further, after asecond buffer layer, the phase-change material, and the second metalfilm are sequentially formed on the semiconductor substrate, the secondmetal film, the phase-change material and the second buffer layer aresequentially etched along the first direction to be processed into astripe shape. Subsequently, after a third interlayer film having a lowerthermal conductivity than the first or second interlayer film is formedon the semiconductor substrate to fill between the adjacent stackedpatterns of the second metal film, the phase-change material, and thesecond buffer layer, a surface of the third interlayer film is polishedto expose an upper surface of the second metal film. Subsequently, thesecond metal film, the phase-change material, and the second bufferlayer are sequentially etched along the second direction to be processedinto a stripe shape. Subsequently, after a fourth interlayer film havinga lower thermal conductivity than the first or second interlayer film isformed on the semiconductor substrate to fill between the adjacentstacked patterns of the second metal film, the phase-change material,and the second buffer layer, a surface of the fourth interlayer film ispolished to expose the upper surface of the second metal film.Subsequently, a third metal film is formed on the semiconductorsubstrate and processed into a stripe shape along the second direction.

The effects obtained by typical aspects of the present invention will bebriefly described below.

It is possible to realize a memory cell structure in which a diode isless likely to be at a high temperature even when a phase-changematerial is set at a high temperature.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a top view of a memory matrix of a phase-change memoryaccording to a first embodiment of the present invention;

FIG. 2 is a cross-sectional view of main parts of the memory matrixtaken along the line of FIG. 1;

FIG. 3 is a cross-sectional view of main parts of the memory matrixtaken along the line B-B′ of FIG. 1;

FIG. 4 is a cross-sectional view of main parts of the memory matrixtaken along the line C-C′ of FIG. 1;

FIG. 5 is a cross-sectional view of main parts of the memory matrixtaken along the line D-D′ of FIG. 1;

FIG. 6 is a top view of the memory matrix showing a manufacturingprocess of the phase-change memory according to the first embodiment ofthe present invention;

FIG. 7 is a cross-sectional view of main parts of the memory matrixcorresponding to the line B-B′ of FIG. 1;

FIG. 8 is a cross-sectional view (B-B′ line) of main parts of thephase-change memory in the manufacturing process continued from FIG. 6and FIG. 7;

FIG. 9 is a cross-sectional view (B-B′ line) of main parts of thephase-change memory in another manufacturing process continued from FIG.6 and FIG. 7;

FIG. 10 is a cross-sectional view (B-B′ line) of main parts of thephase-change memory in still another manufacturing process continuedfrom FIG. 6 and FIG. 7;

FIG. 11 is a cross-sectional view (B-B′ line) of main parts of thephase-change memory in the manufacturing process continued from FIG. 8;

FIG. 12 is a top view of the phase-change memory in the manufacturingprocess continued from FIG. 11;

FIG. 13 is a cross-sectional view (B-B′ line) of main parts of thephase-change memory in the manufacturing process continued from FIG. 11;

FIG. 14 is a cross-sectional view (A-A′ line) of main parts of thephase-change memory in the manufacturing process continued from FIG. 11;

FIG. 15 is a cross-sectional view (A-A′ line) of main parts of thephase-change memory in the manufacturing process continued from FIG. 12,FIG. 13, and FIG. 14;

FIG. 16 is a cross-sectional view (A-A′ line) of main parts of thephase-change memory in the manufacturing process continued from FIG. 15;

FIG. 17 is a configuration diagram of main parts of an equivalentcircuit of the memory matrix of the first embodiment;

FIG. 18 is a cross-sectional view of main parts of the phase-changememory in the case where the memory matrix of the first embodiment isstacked into two layers;

FIG. 19 is a cross-sectional view of main parts of the phase-changememory along a word-line pattern in the case where the memory matrix ofthe first embodiment is stacked into four layers;

FIG. 20 is a cross-sectional view of main parts of the phase-changememory along a bit-line pattern in the case where the memory matrix ofthe first embodiment is stacked into four layers;

FIG. 21 a cross-sectional view of main parts of the phase-change memoryalong the word-line pattern in the case where the memory matrix of thefirst embodiment is stacked into four layers;

FIG. 22 is a cross-sectional view of main parts of the phase-changememory along the bit-line pattern in the case where the memory matrix ofthe first embodiment is stacked into four layers;

FIG. 23 is a top view of a memory matrix of a phase-change memoryaccording to a second embodiment of the present invention;

FIG. 24 is a cross-sectional view of main parts of the memory matrixtaken along the line of FIG. 23;

FIG. 25 is a cross-sectional view of main parts of the memory matrixtaken along the line B-B′ of FIG. 23;

FIG. 26 is a cross-sectional view (B-B′ line) of main parts of thememory matrix showing a manufacturing process of the phase-change memoryaccording to the second embodiment of the present invention;

FIG. 27 is a cross-sectional view (B-B′ line) of main parts of thephase-change memory in the manufacturing process continued from FIG. 26;

FIG. 28 is a cross-sectional view (B-B′ line) of main parts of thephase-change memory in the manufacturing process continued from FIG. 27;

FIG. 29 is a top view of the phase-change memory in the manufacturingprocess continued from FIG. 28;

FIG. 30 is a cross-sectional view (B-B′ line) of main parts of thephase-change memory in the manufacturing process continued from FIG. 28;

FIG. 31 is a cross-sectional view (A-A′ line) of main parts of thephase-change memory in the manufacturing process continued from FIG. 28;

FIG. 32 is a cross-sectional view line) of main parts of thephase-change memory in the manufacturing process continued from FIG. 29,FIG. 30, and FIG. 31;

FIG. 33 is a cross-sectional view of main parts of the phase-changememory in the case where the memory matrix of the second embodiment isstacked into two layers;

FIG. 34 is a cross-sectional view of main parts of the phase-changememory along a word-line pattern in the case where the memory matrix ofthe first embodiment is stacked into four layers;

FIG. 35 is a cross-sectional view of main parts of the phase-changememory along a bit-line pattern in the case where the memory matrix ofthe first embodiment is stacked into four layers;

FIG. 36 is a cross-sectional view (A-A′ line) of main parts of thememory matrix showing another manufacturing process of the phase-changememory according to second embodiment continued from FIG. 26;

FIG. 37 is a cross-sectional view (A-A′ line) of main parts of thephase-change memory in the manufacturing process continued from FIG. 36;

FIG. 38 is a top view of a memory matrix of a phase-change memoryaccording to a third embodiment of the present invention;

FIG. 39 is a cross-sectional view of main parts of the memory matrixtaken along the line A-A′ of FIG. 38;

FIG. 40 is a cross-sectional view of main parts of the memory matrixtaken along the line B-B′ of FIG. 38;

FIG. 41 is a cross-sectional view (B-B′ line) of main parts of thememory matrix showing a manufacturing process of the phase-change memoryof the third embodiment;

FIG. 42 is a cross-sectional view (B-B′ line) of main parts of thephase-change memory in the manufacturing process continued from FIG. 41;

FIG. 43 is a top view of the phase-change memory in the manufacturingprocess continued from FIG. 42;

FIG. 44 is a cross-sectional view (B-B′ line) of main parts of thephase-change memory in the manufacturing process continued from FIG. 42;

FIG. 45 is a cross-sectional view (A-A′ line) of main parts of thephase-change memory in the manufacturing process continued from FIG. 42;

FIG. 46 is a cross-sectional view (A-A′ line) of main parts of thephase-change memory in the manufacturing process continued from FIG. 43,FIG. 44, and FIG. 45;

FIG. 47 is a top view of a memory matrix of a phase-change memoryaccording to a fourth embodiment of the present invention;

FIG. 48 is a cross-sectional view of main parts of the memory matrixtaken along the line A-A′ of FIG. 47;

FIG. 49 is a cross-sectional view of main parts of the memory matrixtaken along the line B-B′ of FIG. 47;

FIG. 50 is a top view of the memory matrix showing a manufacturingprocess of the phase-change memory according to the fourth embodiment;

FIG. 51 is a cross-sectional view of main parts of the memory matrixtaken along the line B-B′ of FIG. 50;

FIG. 52 is a cross-sectional view of main parts of the memory matrixtaken along the line of FIG. 50;

FIG. 53 is a top view of the phase-change memory in the manufacturingprocess continued from FIG. 50, FIG. 51, and FIG. 52;

FIG. 54 is a cross-sectional view of main parts of the memory matrixtaken along the line of FIG. 53;

FIG. 55 is a top view of the phase-change memory in the manufacturingprocess continued from FIG. 53 and FIG. 54;

FIG. 56 is a cross-sectional view of main parts of the memory matrixtaken along the line A-A′ of FIG. 55; and

FIG. 57 is cross-sectional view of main parts of a memory matrix of aphase-change memory studied by the inventors of the present invention.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

In the embodiments described below, the invention will be described in aplurality of sections or embodiments when required as a matter ofconvenience. However, these sections or embodiments are not irrelevantto each other unless otherwise stated, and the one relates to the entireor a part of the other as a modification example, details, or asupplementary explanation thereof.

Also, in the embodiments described below, when referring to the numberof elements (including number of pieces, values, amount, range, and thelike), the number of the elements is not limited to a specific numberunless otherwise stated or except the case where the number isapparently limited to a specific number in principle. The number largeror smaller than the specified number is also applicable. Further, in theembodiments described below, it goes without saying that the components(including element steps) are not always indispensable unless otherwisestated or except the case where the components are apparentlyindispensable in principle. Similarly, in the embodiments describedbelow, when the shape of the components, positional relation thereof,and the like are mentioned, the substantially approximate and similarshapes and the like are included therein unless otherwise stated orexcept the case where it can be conceived that they are apparentlyexcluded in principle. The same goes for the numerical value and therange described above.

Also, in some drawings used in the embodiments, hatching is used even ina plan view so as to make the drawings easy to see. In the embodimentsbelow, “wafer” is mainly a single crystal Si (silicon) wafer, but notonly this, it may be an SOI (Silicon On Insulator) wafer, an insulatingfilm substrate for forming an integrated circuit thereon, etc. A shapeof a wafer is not limited to circular or substantially circular, and itincludes a square shape, a rectangular shape, etc.

Moreover, components having the same function are denoted by the samereference symbols throughout the drawings for describing the embodiment,and the repetitive description thereof will be omitted. Hereinafter,embodiments of the present invention will be described in detail withreference to the accompanying drawings.

First, a basic structure and a basic operation of a phase-change memorystudied by the present inventors will be briefly described since astructure of a phase-change memory according to the embodiments of thepresent invention may be clearer. In the following descriptions, aphase-change memory cell studied by the present inventors will beconveniently called as a conventional phase-change memory cell.

FIG. 57 illustrates a cross-sectional view of main parts of theconventional phase-change memory. In FIG. 57, 101 denotes asemiconductor substrate and 102 denotes a first metal wiring extendingalong a first direction. Further, 103 denotes a first polycrystallinesilicon film, 104 denotes a second polycrystalline silicon film, 105denotes a third polycrystalline silicon film, and the three layers forma diode CDIOD that is a selection element. Further, 106 denotes a bufferlayer, 107 denotes a phase-change material that is a memory element, 108denotes a plug-shaped second metal wiring, 109 denotes a third metalwiring extending along a second direction orthogonal to the firstdirection, and 110 denotes an interlayer film.

In a rewrite operation of the conventional phase-change memory, acurrent sequentially flows from the third metal wiring 109 through thesecond metal wiring 108, the phase-change material 107, the buffer layer106, the diode CDIOD and then to the first metal wiring 102. In thesystem of them, the Joule heat is generated mainly at a portion having ahigh resistance, that is, at the phase-change material 107, an interfacebetween the diode DIOD and the buffer 106, or at an interface betweenthe diode DIOD and the first metal wiring 102. The generated heatdiffuses into surrounding materials. For example, the heat generated inthe phase-change material 107 diffuses into the buffer layer 106, thesecond metal wiring 108, and the interlayer 110 present around thephase-change material 107.

First Embodiment

A memory matrix of a phase-change memory according to a first embodimentwill be described with reference to FIG. 1 to FIG. 5. FIG. 1 is a topview of the memory matrix, FIG. 2 is a cross-sectional view of mainparts of the memory matrix taken along the line A-A′ of FIG. 1, FIG. 3is a cross-sectional view of main parts of the memory matrix taken alongthe line B-B′ of FIG. 1, FIG. 4 is a cross-sectional view of main partsof the memory matrix taken along the line C-C′ of FIG. 1, and FIG. 5 isa cross-sectional view of main parts of the memory matrix taken alongthe line D-D′ of FIG. 1. In FIG. 1, only a third metal wiring, a firstmetal wiring and a semiconductor substrate are illustrated forfacilitating understanding of the structure of the memory matrix.

In the figures, reference numeral 1 denotes a semiconductor substrateand reference numeral 2 denotes a first metal wiring extending along afirst direction. Further, reference numeral 3 denotes a firstpolycrystalline silicon film, reference numeral 4 denotes a secondpolycrystalline silicon film, reference numeral 5 denotes a thirdpolycrystalline silicon film, and the three layers form a diode DIODthat is a selection element. Furthermore, reference numeral 6 denotes abuffer layer (e.g., TiN), reference numeral denotes a phase-changematerial that is a memory element (such as Ge₂Sb₂Te₅), reference numeral8 denotes a second metal wiring (e.g., TiN), reference numeral 9 denotesa third metal wiring, reference numeral 10 denotes a first interlayerfilm (e.g., TEOS: tetraethoxysilane), reference numeral 11 denotes asecond interlayer film (e.g., TEOS), and reference numerals 12 a and 12b denote a void. The first interlayer film 10 and the second interlayerfilm 11 are formed in different regions from each other, whichelectrically isolate the diode DIOD and phase-change material etc.adjacent to each other.

In a rewrite operation of the phase-change memory, similarly to acurrent path of the conventional phase-change memory described above, acurrent sequentially flows from the third metal wiring 9 through thesecond metal wiring 8, the phase-change material 7, the buffer layer 6,and the diode DIOD to the first metal wiring 2.

In the conventional phase-change memory, a thermal conductivity K_(CP)between the memory cells in a layer CPHL in which the phase-changematerial 107 is provided is equal to a thermal conductivity K_(CD)between the memory cells in a layer CDIL in which the diode CDIOD isprovided. In the phase-change memory according to the first embodiment,the first interlayer film 10 or the second interlayer film 11 is presentbetween the adjacent memory cells in a layer DIL in which the diode DIODis provided, and the first interlayer film 10 and the voids 12 a, or thesecond interlayer film 11 and the voids 12 b are present between theadjacent memory cells in a layer PHL in which the phase-change material7 is provided. Here, a thermal conductivity of the first interlayer film10 and the second interlayer film 11 is K_(I) (thermal conductivity ofTEOS: about 1.4 W/(m·K)), and a thermal conductivity of the voids 12 aand 12 b is K_(A) (thermal conductivity of vacuum: about 0 W/(cm·K)),having a relationship of K_(A)<K_(I). Thus, a thermal conductivity K_(P)between the memory cells in the layer PHL in which the phase-changematerial 7 is provided is smaller than a thermal conductivity K_(D)between the memory cells in the layer DIL in which the diode DIOD isprovided.

Therefore, in the phase-change memory according to the first embodiment,heat dissipation is larger in the diode portion and heat dissipation issmaller in the phase-change material portion as compared with theconventional phase-change memory. In other words, the memory matrixaccording to the first embodiment is configured such that the diode DIODis less likely to be at a high temperature and the phase-change material7 is likely to at a high temperature.

Next, a method of manufacturing the phase-change memory according to thefirst embodiment will be described with reference to FIGS. 6 to 16.FIGS. 6 and 12 are top views of the memory matrix, FIGS. 7 to 11 andFIG. 13 are cross-sectional views of main parts of the memory matrixcorresponding to the line B-B′ of FIG. 1, and FIGS. 14 to 16 arecross-sectional views of main parts of the memory matrix correspondingto the line A-A′ of FIG. 1.

At first, as shown in FIGS. 6 and 7, a first metal film 2 a, the firstpolycrystalline silicon film 3, the second polycrystalline silicon film4, the third polycrystalline silicon film 5, the buffer layer 6, thephase-change material 7, and a second metal film 8 a are sequentiallydeposited on the semiconductor substrate 1.

A material of the first metal film 2 a is formed of W (tungsten) forexample, and it can be formed by a CVD (Chemical Vapor Deposition)method or the like for example. When the first polycrystalline siliconfilm 3 is formed of polycrystalline silicon containing B (boron) as animpurity, since the first polycrystalline silicon film 3 and the firstmetal film 2 a are configured to be directly joined, it is desirable tolower a contact resistance between the first polycrystalline siliconfilm 3 and the first metal film 2 a with setting the material of thefirst metal film 2 a as W. A film thickness of the first metal film 2 ais desirably in a range of 10 to 100 nm, for example. When the filmthickness of the first metal film 2 a is too thin, a wiring resistancebecomes high, and when it is too thick, the processing shape becomesdifficult to control.

A material of the first polycrystalline silicon film 3 ispolycrystalline silicon containing any of B, Ga (gallium) or In (indium)as an impurity, a material of the second polycrystalline silicon film 4is intrinsic polycrystalline silicon, and a material of the thirdpolycrystalline silicon film 5 is polycrystalline silicon containing P(phosphorous) or As (arsenic) as an impurity. They can be formed by, forexample, a CVD method, respectively. A total film thickness of the firstpolycrystalline silicon film 3, the second polycrystalline silicon film4 and the third polycrystalline silicon film 5 is desirably in a rangeof 30 to 250 nm, for example.

The first polycrystalline silicon film 3, the second polycrystallinesilicon film 4 and the third polycrystalline silicon film 5 may becrystallized to be formed by laser annealing after being formed asamorphous silicon instead of being formed as polycrystalline siliconfrom the beginning. Thus, it is possible to reduce a thermal load duringthe process. While the PIN diode has been exemplified as the selectionelement, P⁺/N⁻/N⁺ diode may be used, by which the same performance asthe PIN diode can be accomplished. Tungsten silicide or titaniumsilicide may be formed by using a silicidation technique on the firstpolycrystalline silicon film 3 and the first metal film 2 a in order toreduce the contact resistance. Similarly, titanium silicide or the likemay be formed between the third polycrystalline silicon film 5 and thebuffer layer 6.

A material of the buffer layer 6 is TiN for example, and it can beformed by a CVD method or the like for example. The buffer layer 6 isprovided in order to prevent the first polycrystalline silicon film 3,the second polycrystalline silicon film 4, the third polycrystallinesilicon film 5 and the phase-change material 7 from interdiffusion, anda film thickness of the buffer layer 6 is desirably 50 nm or less sincea driving voltage of the phase-change memory increases if the thicknessis too large.

The phase-change material 7 is Ge₂Sb₂Te₅ for example, and it can beformed by a sputtering method or the like for example. The phase-changematerial 7 may use a material containing at least one element from amongchalcogen elements (S, Se, Te), and can obtain the same performance asGe₂Sb₂Te₅ according to the selection of the composition. A filmthickness of the phase-change material 7 is desirably in a range of 5 to300 nm, for example.

A material of the second metal film 8 a is TiN for example, and it canbe formed by a CVD method or the like for example. A film thickness ofthe second metal film 8 a is desirably in a range of 10 to 100 nm, forexample. When the film thickness of the second metal film 8 a is toosmall, a grinding margin will be deficient in a later CMP (ChemicalMechanical Polishing) step, while when it is too large, the drivingvoltage of the phase-change memory increases. Further, the material ofthe buffer layer 6 and the second metal wiring 8 a is desirably amaterial having a low thermal conductivity. When a material having a lowthermal conductivity is used, the driving voltage of the phase-changememory can be reduced.

Next, as shown in FIG. 8, a lithography technique and a dry etchingtechnique are used to sequentially process the second metal film 8 a,the phase-change material 7, the buffer layer 6, the thirdpolycrystalline silicon film 5, the second polycrystalline silicon film4, the first polycrystalline silicon film 3, and the first metal film 2a, along the first direction. Thus, the first metal wiring 2 formed ofthe first metal film 2 a is formed. A stacked pattern formed of thesecond metal film 8 a, the phase-change material 7, the buffer layer 6,the third polycrystalline silicon film 5, the second polycrystallinesilicon film 4, the first polycrystalline silicon film 3, and the firstmetal wiring 2 is a pattern of a word line, and is formed into a stripeshape along the first direction in parallel with an adjacent pattern.Further, the first metal wiring 2 is electrically connected to thesemiconductor substrate 1 including a peripheral circuit such that aread operation and a write operation of the phase-change memory can beperformed (illustration is omitted).

It is preferred that a width of the phase-change material 7 is narrowerthan the widths of the lower buffer layer 6, the third polycrystallinesilicon film 5, the second polycrystalline silicon film 4 and the firstpolycrystalline silicon film 3, and a width of the second metal film 2 ais wider than the width of the phase-change material 7. This is foreasily forming a void described later. Further, since the smaller avolume of the phase-change material 7 is, the more the drive voltage ina rewrite operation of the phase-change material 7 can be reduced, it ispreferred to reduce the volume of the phase-change material 7.

Regarding a method for making the width of the phase-change material 7narrower than other portions, there is a method in which the secondmetal film 8 a is first processed by an anisotropic dry etching, and thephase-change material 7 is subsequently processed by an isotropic dryetching, and then the buffer layer 6, the third polycrystalline siliconfilm 5, the second polycrystalline silicon film 4, the firstpolycrystalline silicon film 3 and the first metal film 2 a aresequentially processed by an anisotropic dry etching.

As shown in FIG. 9, there is a method in which the second metal film 8 aand the phase-change material 7 are first sequentially processed byanisotropic dry etching, and subsequently the phase-change material 7 isprocessed by isotropic dry etching to apply side etching on a sidesurface of the phase-change material 7. Then, the buffer layer 6, thethird polycrystalline silicon film 5, the second polycrystalline siliconfilm 4, the first polycrystalline silicon film 3, and the first metalfilm 2 a are sequentially processed again by anisotropic dry etching.

As shown in FIG. 10, there is a method in which the second metal film 8a, the phase-change material 7, the buffer layer 6, the thirdpolycrystalline silicon film 5, the second polycrystalline silicon film4, the first polycrystalline silicon film 3, and the first metal film 2a are first sequentially processed by anisotropic dry etching and thenside etching is selectively applied on the side surface of thephase-change material 7.

Next, as shown in FIG. 11, the first interlayer film 10 is formed on thesemiconductor substrate 1. A material of the first interlayer film 10 isTEOS for example, and can be formed by a CVD method and the like forexample. Since a width of the phase-change material 7 is narrower thanthat of the third polycrystalline silicon film 5, the secondpolycrystalline silicon film 4 and the first polycrystalline siliconfilm 3 and a width of the second metal film 8 a is wider than the widthof the phase-change material 7, the first interlayer film 10 is formedby using conditions under which the film formation is isotropicallyperformed so that the voids 12 a are simultaneously formed between theadjacent stacked patterns of the second metal film 8 a, the phase-changematerial 7, the buffer layer 6, the third polycrystalline silicon film5, the second polycrystalline silicon film 4, the first polycrystallinesilicon film 3, and the first metal wiring 2. Alternatively, once thefirst interlayer film 10 is filled to a certain degree between theadjacent stacked patterns of the third polycrystalline silicon film 5,the second polycrystalline silicon film 4, the first polycrystallinesilicon film 3, and the first metal wiring 2 by using film formationconditions with excellent filling characteristics, the first interlayerfilm 10 may be filled between the adjacent stacked patterns of thesecond metal film 8 a and the phase-change material 7 by usingconditions with bad filling characteristics.

Next, as shown in FIGS. 12, 13 and 14, a CMP technique is used to polisha surface of the first interlayer film 10 to expose a surface of thesecond metal film 8 a. FIG. 12 is a top view of the memory matrix, whereonly the second metal film 8 a and the semiconductor substrate 1 areillustrated for facilitating understanding of the structure of thememory matrix. Further, FIG. 13 is a cross-sectional view of main partsof the memory matrix taken along the like B-B′ of FIG. 12, and FIG. 14is a cross-sectional view of main parts of the memory matrix taken alongthe line A-A′ of FIG. 12.

Next, as shown in FIG. 15, the third metal film 9 a is formed on thesemiconductor substrate 1. A material of the third metal film 9 a is W,for example, and can be formed by a CVD method or the like, for example.A total film thickness of the second metal film 8 a and the third metalfilm 9 a is preferred to be 200 nm or less, for example. When the filmthickness is larger than 200 nm, the second metal film 8 a and the thirdmetal film 9 a are difficult to process by dry etching.

Next, as shown in FIG. 16, the lithography technique and the dry etchingtechnique are used to sequentially process the third metal film 9 a, thesecond metal film 8 a, the phase-change material 7, the buffer layer 6,the third polycrystalline silicon film 5, the second polycrystallinesilicon film 4, and the first polycrystalline silicon film 3 along asecond direction. Thus, the third metal wiring 9 formed of the thirdmetal film 9 a is formed, and the plug-shaped second metal wiring 8formed of the second metal film 8 a is formed. Further, the diode DIODis formed having a stacked structure including the third polycrystallinesilicon film 5, the second polycrystalline silicon film 4, and the firstpolycrystalline silicon film 3. A stacked pattern of the third metalwiring 9, the second metal wiring 8, the phase-change material 7, thebuffer layer 6, the third polycrystalline silicon film 5, the secondpolycrystalline silicon film 4, and the first polycrystalline siliconfilm 3 is a pattern of a bit line, and is formed into a stripe shapealong the second direction orthogonal to the first direction and inparallel with the adjacent pattern. Further, the third metal wiring 9 iselectrically connected (not shown) to the semiconductor substrate 1including a peripheral circuit so that read and write operation of thephase-change memory can be performed. Further, similarly to the methodexplained above in FIGS. 8 to 10, the width of the phase-change material7 is processed to be narrower than the widths of the lower buffer layer6, the third polycrystalline silicon film 5, the second polycrystallinesilicon film 4 and the first polycrystalline silicon film 3, and thewidths of the third metal wiring 9 and the second metal wiring 8 areprocessed to be wider than the width of the phase-change material 7.

Thereafter, the second interlayer film 11 is formed on the semiconductorsubstrate 1. A material of the second interlayer film 11 is TEOS forexample, and it can be formed by a CVD method or the like for example.Further, similarly to the voids 12 a described above, the voids 12 b aresimultaneously formed between the adjacent stacked patterns of the thirdmetal wiring 9, the second metal wiring 8, the phase-change material 7,the buffer layer 6, the third polycrystalline silicon film 5, the secondpolycrystalline silicon film 4, the first polycrystalline silicon film 3and the first metal wiring 2. In this manner, the memory cell accordingto the first embodiment shown in FIGS. 1 to 5 described above issubstantially completed. A filling ratio of the first interlayer film 10between the memory cells is, for example, 75% or more in a planeconnecting the center of gravity of the diode DIOD to the center ofgravity of the diode DIOD in the adjacent memory cell, and a fillingratio of the second interlayer film 11 between the memory cells is, forexample, in a range of 75% and 50% in a plane connecting the center ofgravity of the phase-change material 7 to the phase-change material 7 inthe adjacent memory cell.

Next, a method of operation of the memory matrix according to the firstembodiment of the present invention will be described with reference toFIG. 17. FIG. 17 is a configuration diagram of main parts of anequivalent circuit of the memory matrix. Memory cells MCij (i=1, 2, 3, .. . , m) (j=1, 2, 3, . . . , n) are arranged at intersection points of aplurality of first metal wirings arranged in parallel (hereinafter, wordlines) WLi (i=1, 2, 3, . . . , m) with a plurality of third metalwirings (hereinafter, bit lines) BLj (j=1, 2, 3, . . . , n) arranged inparallel to be intersect with the word lines WLi. As shown in FIG. 1described above, the diode DIOD and the phase-change material 7 areconnected in series, and in FIG. 17, the diode DIOD corresponds to aselection element SE and the phase-change material 7 corresponds to amemory element VR.

Recording into the phase-change memory is performed in the followingmanner. For example, in a rewrite operation of the memory cell MC11, avoltage Vh is applied to the first word line WL1, a voltage Vl isapplied to other word lines WLi, the voltage Vl is applied to the firstbit line BL1, and the voltage Vh is applied to other bit lines BLj, sothat a current is flowed to the memory element VR of the MC11 to storeinformation. Here, Vh>Vl. At the time of the rewriting operation, theselection element SE having a rectifying operation is required in orderto prevent erroneous writing into non-selective memory cells. Of course,the voltage Vh has to be smaller than or equal to a breakdown voltage ofthe selection element SE.

Reading of the nonvolatile memory is performed as follows. For example,when information in the memory cell MC11 is read, a voltage Vm isapplied to the first word line WL1, the voltage Vl is applied to otherword lines WLi and the voltage Vl is applied to the first bit line BL1so that the information is read on the basis of a magnitude of thecurrent flowing through the BL1.

It has been described in the first embodiment that the first metalwiring 2 is assumed as a word line and the third metal wiring 9 isassumed as a bit line, but the first metal wiring 2 may be assumed as abit line and the third metal wiring 9 may be assumed as a word line.

It has been described the case in which the memory matrix is one layer,but a stack of the memory matrix is more preferable because the bitdensity of the memory cell can be increased. FIG. 18 shows across-sectional view of main parts of the phase-change memory in thecase where the memory matrix according to the first embodiment isstacked into two layers. For example, the two-layer stack of the memorymatrix can be realized similarly to the manufacturing method describedabove with reference to FIGS. 6 to 16 according to the first embodimentby forming: a first metal wiring 2A as word line at the second layer ofthe memory matrix; a first polycrystalline silicon film 3A at the secondlayer; a second polycrystalline silicon film 4A at the second layer; athird polycrystalline silicon film 5A at the second layer; a bufferlayer 6A at the second layer; a phase-change material 7A at the secondlayer; a second metal wiring 8A at the second layer; a third metalwiring 9A at the second layer; a first interlayer film at the secondlayer (not shown); a second interlayer film 11A at the second layer;voids 12 bA at the second layer; and the like on the structure shown inFIGS. 1 to 5 described above, that is, on the second interlayer film 11.Further, also when the memory matrix is stacked into “k” layers (k=1, 2,3, . . . , 1), the memory matrix may be stacked in the similar manner.

FIGS. 19 and 20 show cross-sectional views of main parts of thephase-change memory when the memory matrix according to the firstembodiment is stacked into four layers. FIG. 19 is a cross-sectionalview of main parts of the phase-change memory along a pattern (word linepattern) of a lower metal wiring A1M1M, a lower metal wiring A1M2M, alower metal wiring A2M3M and a lower metal wiring A2M4M. FIG. 20 is across-sectional view of main parts of the phase-change memory along apattern (bit line pattern) of an upper metal wiring B2M1M, an uppermetal wiring B1M2M, an upper metal wiring B2M3M, and an upper metalwiring B1M4M. In the figures, A1ST, A2ST, B1ST and B2ST denote atransistor for selecting a layer formed by a CMOS (Complementary MetalOxide Semiconductor) technique, for example, and a symbol DIF denotes adiffusion layer and GAT denotes a gate.

For example, connection with a peripheral circuit when stacking thememory matrix into four layers employs the structure of the memorymatrix shown in FIGS. 19 and 20. For example, the transistor A1ST andthe transistor B2ST may be selected when the first layer is selected,and the transistor A1ST and the transistor B1ST may be selected when thesecond layer is selected.

FIGS. 21 and 22 show cross-sectional views of main parts of thephase-change memory when the word lines and the bit lines according tothe first embodiment are shared in each layer. The bit density is thesame as the bit density of the structure described in FIGS. 19 and 20,but when the word lines and the bit lines are shared in each layer,masks necessary for the manufacture can be reduced, thereby reducing amanufacturing cost thereof.

Note that, line/space of the adjacent first metal wiring may be set atthe same value as the line/space of the adjacent third metal wiring 9,and the line/space of the adjacent first metal wiring 2 may be set at adifferent value from the line/space of the adjacent third metal wiring9. For example, the space of the adjacent third metal wiring 9 may beset to be wider than the space of the adjacent first metal wiring 2. Inthis case, the first interlayer film 10 is filled between the adjacentselection element and memory element along the second direction, and atthe same time, the voids 12 a are formed between the adjacent stackedpatterns of the second metal film 8 a, the phase-change material 7, thebuffer layer 6, the third polycrystalline silicon film 5, the secondpolycrystalline silicon film 4, the first polycrystalline silicon film 3and the first metal film wiring 2. Further, the second interlayer film11 is filled between the adjacent selection element and memory elementalong the first direction, and at the same time, the voids 12 b areformed between the adjacent stacked patterns of the third metal wiring9, the second metal wiring 8, the phase-change material 7, the bufferlayer 6, the third polycrystalline silicon film 5, the secondpolycrystalline silicon film 4 and the first polycrystalline siliconfilm 3. Therefore, a filled state upon forming the first interlayer film10 may be different from a filled state upon forming the secondinterlayer film 11, and in some cases, the space of the adjacent thirdmetal wiring 9 may be necessary to be wider than the space of theadjacent first metal wiring 2 in order to control the shape of the voids12 a and 12 b.

In this manner, according to the first embodiment, the first interlayerfilm 10 or the second interlayer film 11 formed of, for example, TEOS isfilled at the layer DIL in which the diode DIOD (stacked pattern of thethird polycrystalline silicon film 5, the second polycrystalline siliconfilm 4 and the first polycrystalline silicon film 3) is provided. On theother hand, the first interlayer film 10 in which the voids 12 a areformed or the second interlayer film 11 in which the voids 12 b areformed is filled at the layer PHL in which the phase-change material 7is provided, and it is thus possible to reduce a transfer of heatgenerated in the phase-change material 7 to the diode DIOD. Accordingly,even when the phase-change material 7 becomes a high temperature, it ispossible to realize the memory cell structure in which the diode DIOD isless likely to be at a high temperature.

Second Embodiment

A memory matrix of a phase-change memory according to a secondembodiment will be described with reference to FIGS. 23 to 25. FIG. 23is a top view of the memory matrix, FIG. 24 is a cross-sectional view ofmain parts of the memory matrix taken along the line A-A′ of FIG. 23,and FIG. 25 is a cross-sectional view of main parts of the memory matrixtaken along the line B-B′ of FIG. 23. In FIG. 23, only a third metalwiring 9, a first metal wiring 2, and a semiconductor substrate 1 areillustrated for facilitating understanding of the structure of thememory matrix. In the figures, similarly as in the first embodimentdescribed above, reference numeral 1 denotes a semiconductor substrateand reference numeral 2 denotes a first metal wiring extending along afirst direction. Further, reference numeral 3 denotes a firstpolycrystalline silicon film, reference numeral 4 denotes a secondpolycrystalline silicon film, reference numeral 5 denotes a thirdpolycrystalline silicon film, where the three layers form a diode DIODas a selection element. Reference numeral 6 denotes a buffer layer(e.g., TiN), reference numeral 7 denotes a phase-change material (e.g.,Ge₂Sb₂Te₅) as a memory element, reference numeral 8 denotes a secondmetal wiring (e.g., TiN), and reference numeral 9 denotes a third metalwiring. Furthermore, reference numeral 21 denotes a first interlayerfilm (e.g., TEOS), reference numeral 22 denotes a second interlayer film(e.g., porous MSQ (Methylsilses-quioxane)) which fills a space occurringdue to a coating form of the first interlayer film, reference numeral 23denotes a third interlayer film (e.g., TEOS), and reference numeral 24denotes a fourth interlayer film (e.g., porous MSQ) which fills a spaceoccurring due to a coating form of the third interlayer film. A thermalconductivity of TEOS is about 1.4 W/(m·K) and a thermal conductivity ofporous MSQ is about 0.2 W/(m·K).

In the phase-change memory according to the second embodiment, the firstinterlayer film 21 or the third interlayer film 23 is present betweenthe memory cells being adjacent at the layer DIL in which the diode DIODis provided, and, the sidewall-shaped first interlayer film 21 and thesecond interlayer film 22 to fill a space occurring due to the sidewallshape of the first interlayer film 21, or the sidewall-shaped thirdinterlayer film 23 and the fourth interlayer film 24 to fill a spaceoccurring due to the sidewall shape of the third interlayer film 23 arepresent between the adjacent memory cells at the layer PHL in which thephase-change material 7 is provided. When a thermal conductivity of thefirst interlayer film 21 and the third interlayer film 23 is assumed tobe K_(n) and a thermal conductivity of the second interlayer film 22 andthe fourth interlayer film 24 is assumed to be K_(I2), if K_(I2)<K_(I1),a thermal conductivity K_(P1) between the memory cells at the layer PHLin which the phase-change material 7 is provided is smaller than athermal conductivity K_(D1) between the memory cells at the layer DIL inwhich the diode DIOD is provided, thereby forming a memory cell having astructure in which the diode DIOD is less likely to be at a hightemperature and the phase-change material 7 is likely to at a hightemperature. To the contrary, if K_(I2)>K_(I1), the thermal conductivityK_(P1) between the memory cells in the layer PHL in which thephase-change material 7 is provided is larger than the thermalconductivity K_(D1) between the memory cells in the layer DIL in whichthe diode DIOD is provided, but it is possible to form a memory cell inwhich the phase-change material 7 is cooled down more rapidly so that ahigh-speed operation is enabled. In the second embodiment, the materialsbetween the memory cells in the layer PHL in which the phase-changematerial 7 is provided have been described by the two types of the firstinterlayer film 21 and the second interlayer film 22 or the two types ofthe third interlayer film 23 and the fourth interlayer film 24, butthree or more types of materials may be used. Importantly, the thermalconductivity K_(P1) between the memory cells in the layer PHL in whichthe phase-change material 7 is provided is different from the thermalconductivity K_(D1) between the memory cells in the layer DIL in whichthe diode DIOD is provided.

Next, a method of manufacturing the phase-change memory according to thesecond embodiment will be described with reference to FIGS. 26 to 32.FIG. 29 is a top view of the memory matrix, FIGS. 26 to 28 and FIG. 30are cross-sectional views of main parts of the memory matrix taken alongthe line B-B′ of FIG. 23, and FIGS. 31 and 32 are cross-sectional viewsof main parts of the memory matrix taken along the line A-A′ of FIG. 23.

At first, from the structure of the first embodiment described aboveshown in FIGS. 6 and 7, the lithography technique and the dry etchingtechnique are used to sequentially process the second metal film 8 a,the phase-change material 7, the buffer layer 6, the thirdpolycrystalline silicon film 5, the second polycrystalline silicon film4, the first polycrystalline silicon film 3 and the first metal film 2 ainto a stripe shape along the first direction. In this manner, as shownin FIG. 26, the first metal wiring 2 formed of the first metal film 2 ais formed.

The widths of the second metal film 8 a and the phase-change material 7are preferably narrower than the widths of the lower buffer layer 6, thethird polycrystalline silicon film 5, the second polycrystalline siliconfilm 4 and the first polycrystalline silicon film 3. This is directedfor easily forming two or more types of interlayer films to be describedlater. A method of making the widths of the second metal film 8 a andthe phase-change material 7 narrower than other portions includes: amethod in which the second metal film 8 a and the phase-change material7 are first processed to be thin by isotropic dry etching and then thebuffer layer 6, the third polycrystalline silicon film 5, the secondpolycrystalline silicon film 4, the first polycrystalline silicon film 3and the first metal film 2 a are processed by anisotropic dry etching; amethod in which, as shown in FIG. 9 according to the first embodimentdescribed above, the second metal film 8 a and the phase-change material7 are sequentially processed by anisotropic dry etching and subsequentlythe second metal film 8 a and the phase-change material 7 are processedto be thin by isotropic dry etching and then the buffer layer 6, thethird polycrystalline silicon film 5, the second polycrystalline siliconfilm 4, the first polycrystalline silicon film 3 and the first metalfilm 2 a are sequentially processed again by anisotropic dry etching;and the like.

Next, as shown in FIG. 27, the first interlayer film 21 is formed on thesemiconductor substrate 1. The material of the first interlayer film 21is TEOS for example, and can be formed by CVD or the like for example.The widths of the second metal film 8 a and the phase-change material 7are narrower than the widths of the buffer layer 6, the thirdpolycrystalline silicon film 5, the second polycrystalline silicon film4, the first polycrystalline silicon film 3 and the first metal wiring2. Thus, the conditions under which the film is isotropically formed areused to form the first interlayer film 21 so that the first interlayerfilm 21 is filled between the adjacent stacked patterns of the bufferlayer 6, the third polycrystalline silicon film 5, the secondpolycrystalline silicon film 4, the first polycrystalline silicon film 3and the first metal wiring 2, but the sidewall-shaped first interlayerfilm 21 is formed between the adjacent stacked patterns of the secondmetal film 8 a and the phase-change material 7 so that a space is formedinstead of being filled with the first interlayer film 21.

Next, as shown in FIG. 28, the first interlayer film 21 is etched backuntil the surface of the second metal film 8 a is exposed. Through theetching-back, the first interlayer film 21 filled between the adjacentstacked patterns of the buffer layer 6, the third polycrystallinesilicon film 5, the second polycrystalline silicon film 4, the firstpolycrystalline silicon film 3 and the first metal wiring 2 can beremoved more deeply, for example, down to around the buffer layer 6 sothat a space in which the interlayer film 21 is not formed can be formedeven between the adjacent stacked patterns of the second metal film 8 a,the phase-change material 7 and the buffer layer 6.

In addition, as shown in FIGS. 29, 30 and 31, after the secondinterlayer film 22 is deposited on the semiconductor substrate 1, theCMP technique is used to polish the surface of the second interlayerfilm 22 to expose the surface of the second metal film 8 a. The materialof the second interlayer film 22 is porous MSQ, for example, and can beformed by a coating method, for example. In the second embodiment, thefilling depth of the second interlayer film 22 can be adjusted by theetching-back so that materials having different thermal conductivitiescan be accurately arranged between the memory cells. FIG. 29 is a topview of the memory matrix, where only the second metal film 8 a, thefirst metal wiring 2 and the semiconductor substrate 1 are illustratedfor facilitating understanding of the structure of the memory matrix.FIG. 30 is a cross-sectional view of main parts of the memory matrixtaken along the line B-B′ of FIG. 29, and FIG. 31 is a cross-sectionalview of main parts of the memory matrix taken along the line A-A′ ofFIG. 29.

Next, after a third metal film (same metal film as the third metal film9 a used in the first embodiment described above) is formed on thesemiconductor substrate 1, the lithography technique and the dry etchingtechnique are used to sequentially process the third metal film, thesecond metal film 8 a, the phase-change material 7, the buffer layer 6,the third polycrystalline silicon film 5, the second polycrystallinesilicon film 4 and the first polycrystalline silicon film 3 into astripe shape along the second direction. In this manner, as shown inFIG. 32, the third metal wiring 9 formed of the third metal film isformed so that the plug-shaped second metal wiring 8 formed of thesecond metal film 8 a is formed. The material of the third metal wiring9 is W for example, and can be formed by a CVD method or the like, forexample. A total film thickness of the second metal wiring 8 and thethird metal wiring 9 is preferably 200 nm or less. If it is too thick,the processing becomes difficult.

Thereafter, similarly as the manufacturing method described above withreference to FIGS. 27 to 31, the third interlayer film 23 and the fourthinterlayer film 24 are formed. In this manner, the phase-change memoryaccording to the second embodiment shown in FIGS. 23 to 25 describedabove is substantially completed. The filling ratio of the secondinterlayer film 22 or the fourth interlayer film 24 between the memorycells is 25% or less in a plane connecting the center of gravity of thediode DIOD to the center of gravity of the diode DIOD in the adjacentmemory cell, and the filling ratio of the second interlayer film 22 orthe fourth interlayer film 24 between the memory cells is between 50%and 25% in a plane connecting the center of gravity of the phase-changematerial 7 to the center of gravity of the phase-change material 7 inthe adjacent memory cell.

A method of operation of the memory matrix according to the secondembodiment is similar to the first embodiment described above.

While it has been described the case in which the memory matrix is onelayer in the foregoing, stacking of the memory matrix to enhance the bitdensity is more preferred because it reduces the manufacturing cost.FIG. 33 is a cross-sectional view of main parts of the phase-changememory when the memory matrix according to the second embodiment isstacked into two layers. For example, the stack of the memory matrixinto two layers can be realized similarly as that in the methoddescribed with FIGS. 26 to 32 above for the second embodiment by forminga first metal wiring 2A as word line at the second layer of the memorymatrixes, a first polycrystalline silicon film 3A at the second layer, asecond polycrystalline silicon film 4A at the second layer, a thirdpolycrystalline silicon film 5A at the second layer, a buffer layer 6Aat the second layer, a phase-change material 7A at the second layer, asecond metal wiring 8A at the second layer, a third metal wiring 9A atthe second layer, a first interlayer film at the second layer (notshown), a second interlayer film at the second layer (not shown), athird interlayer film 23A at the second layer, and a fourth interlayerfilm 24A at the second layer on the structure shown in FIGS. 23 to 25described above, that is, on the fourth interlayer film 24. Further,also when the memory matrix is stacked into k layers (k=1, 2, 3, . . . ,1), the memory matrix may be stacked in the similar way.

FIGS. 34 and 35 are cross-sectional views of main parts of thephase-change memory in the case where the memory matrix according to thesecond embodiment is stacked into four layers. FIG. 34 is across-sectional view of main parts of the phase-change memory along apattern (word line pattern) of a lower metal wiring A1M1M, a lower metalwiring A1M2M, a lower metal wiring A2M3M and a lower metal wiring A2M4M,and FIG. 35 is a cross-sectional view of main parts of the phase-changememory along a pattern (bit line pattern) of an upper metal wiringB2M2M, an upper metal wiring B1M3M, an upper metal wiring B2M4M and anupper metal wiring B1M5M. In the figures, A1ST, A2ST, B1ST and B2STdenote a transistor for selecting a layer formed by using the CMOStechnique, for example, and a symbol DIF denotes a diffusion layer andGAT denotes a gate in the figures.

Connections to peripheral circuits when the memory matrix is stackedinto, for example, four layers, has the structure of the memory matrixshown in FIGS. 34 and 35. For example, when the first layer is selected,the transistor A1ST and the transistor B2ST may be selected, while whenthe second stage is selected, the transistor A1ST and the transistorB1ST may be selected.

In the case an interlayer film is filled between the memory cellsaccording to the second embodiment, there has been employed, asdescribed with reference to FIGS. 27 to 30 above, the manufacturingsteps of: forming the first interlayer film 21; processing the firstinterlayer film 21 by the etching method; filling a space occurring dueto the formation of the first interlayer film 21 with the secondinterlayer film 22; and processing the second interlayer film 22 by theCMP method. Meanwhile, the method is not limited to this. For example,manufacturing steps to be described later may be employed in place ofthe manufacturing steps.

At first, as shown in FIG. 36, the first interlayer film 21 is formed onthe semiconductor substrate 1. At this time, the first interlayer film21 is completely filled between the adjacent stacked patterns of thesecond metal film 8 a, the phase-change material 7, the buffer layer 6,the third polycrystalline silicon film 5, the second polycrystallinesilicon film 4, the first polycrystalline silicon film 3, and the firstmetal wiring 2. The material of the first interlayer film 21 is TEOS,for example. Subsequently, the first interlayer film 21 is etched backdown to around the buffer layer G. The second metal film 8 a and thephase-change material 7 are exposed through the etching-back.

Next, as shown in FIG. 37, the second interlayer film 22 is formed onthe semiconductor substrate 1 so that the second interlayer film 22 iscompletely filled between the adjacent stacked patterns of the secondmetal film 8 a and the phase-change material 7. Thereafter, the CMPtechnique is used to polish the surface of the second interlayer film 22to expose the surface of the second metal film 8 a. The material of thesecond interlayer film 22 is porous MSQ for example, and can be formedby a coating method for example.

By using the above-described manufacturing method, the second interlayerfilm 22 having a lower thermal conductivity than the first interlayerfilm 21 can be completely filled between the adjacent stacked patternsof the second metal film 8 a and the phase-change material 7.

In this manner, according to the second embodiment, since a thermalconductivity between the memory cells at the layer DIL in which thediode DIOD (stacked pattern of the third polycrystalline silicon film 5,the second polycrystalline silicon film 4, and the first polycrystallinesilicon film 3) is provided may be set at a different value from athermal conductivity between the memory cells at the layer PHL in whichthe phase-change material 7 is provided, an optimum design of thephase-change memory having desired characteristics can be facilitated.For example, the first interlayer film 21 or the third interlayer film23 formed of, for example, TEOS is filled at the layer DIL in which thediode DIOD (stacked pattern consisting of the third polycrystallinesilicon film 5, the second polycrystalline silicon film 4, and the firstpolycrystalline silicon film 3) is provided, for example, and the firstinterlayer film 21 formed of, for example, TEOS and the secondinterlayer film 22 formed of porous MSQ, or the third interlayer film 23formed of TEOS and the fourth interlayer film 24 formed of porous MSQcan be filled at the layer PHL in which the phase-change material 7 isprovided. Since the interlayer film formed of porous MSQ having a lowerthermal conductivity than TEOS is provided at the layer PHL in which thephase-change material 7 is provided, it is possible to reduce thetransfer of the heat generated in the phase-change material 7 to thediode DIOD as compared with the case in which only the interlayer filmformed of TEOS is provided. In this manner, even when the phase-changematerial 7 is at a high temperature, it is possible to realize thephase-change memory cell in which the diode DIOD is less likely to be ata high temperature.

Third Embodiment

A memory matrix of a phase-change memory according to a third embodimentwill be described with reference to FIGS. 38 to 40. FIG. 38 is a topview of the memory matrix, FIG. 39 is a cross-sectional view of mainparts of the memory matrix taken along the line A-A′ of FIG. 38, andFIG. 40 is a cross-sectional view of main parts of the memory matrixtaken along the line B-B′ of FIG. 38. In FIG. 38, only a third metalwiring, a first metal wiring, and a semiconductor substrate areillustrated for facilitating understanding of a structure of the memorymatrix. In the figures, similarly as those in the first embodimentdescribed above, reference numeral 1 denotes a semiconductor substrateand reference numeral 2 denotes a first metal wiring extending along afirst direction. Further, reference numeral 3 denotes a firstpolycrystalline silicon film, reference numeral 4 denotes a secondpolycrystalline silicon film, reference numeral 5 denotes a thirdpolycrystalline silicon film, and these three layers form a diode DIODas a selection element. Further, reference numeral 6 denotes a bufferlayer (e.g., TiN), reference numeral 7 denotes a phase-change material(e.g., Ge₂Sb₂Te₅) as a memory element, reference numeral 8 denotes asecond metal wiring (e.g., TiN), and reference numeral 9 denotes a thirdmetal wiring. Reference numeral 31 denotes a first interlayer film(e.g., TEOS), reference numeral 32 denotes a second interlayer film(e.g., porous MSQ) fill a space occurring due to a coating form of thefirst interlayer film, reference numeral 33 denotes a third interlayerfilm (e.g., TEOS), and reference numeral 34 denotes a fourth interlayerfilm (e.g., porous MSQ) to fill a space occurring due to a coating shapeof the third interlayer film.

In the phase-change memory according to the third embodiment, the firstinterlayer film 31 or the third interlayer film 33 is present betweenthe adjacent memory cells at a layer DIL in which a diode DIOD isprovided, and the sidewall-shaped first interlayer film 31 and thesecond interlayer film 32 to fill a space occurring due to the sidewallshape of the first interlayer film 31, or the sidewall-shaped thirdinterlayer film 33 and the fourth interlayer film 34 to fill a spaceoccurring due to the sidewall shape of the third interlayer film 33 arepresent between the adjacent memory cells at a layer PHL in which thephase-change material 7 is provided. Therefore, similarly to that in thesecond embodiment described above, a thermal conductivity between thememory cells at the layer PHL in which the phase-change material 7 isprovided may be set at a different value from a thermal conductivitybetween the memory cells at the layer DIL in which the diode DIOD isprovided. For example, when a thermal conductivity of the firstinterlayer film 31 and the third interlayer film 33 is assumed to beK_(I3) and a thermal conductivity of the second interlayer film 32 andthe fourth interlayer film 34 is assumed to be K_(I4), if K_(I4)>K_(I3),a thermal conductivity K_(P2) between the memory cells at the layer PHLin which the phase-change material 7 is provided is smaller than athermal conductivity K_(D2) between the memory cells at the layer DIL inwhich the diode DIOD is provided, thereby forming a memory cell havingthe structure in which the diode DIOD is less likely to be at a hightemperature and the phase-change material 7 is likely to at a hightemperature.

Next, a method for manufacturing the phase-change memory according tothe third embodiment will be described with reference to FIGS. 41 to 46.FIG. 43 is a top view of the memory matrix, FIGS. 41, 42 and 44 arecross-sectional views of main parts of the memory matrix taken along theline B-B′ of FIG. 38, and FIGS. 45 and 46 are cross-sectional views ofmain parts of the memory matrix taken along the line A-A′ of FIG. 38.

At first, as shown in FIG. 41, from the structure of the firstembodiment described above shown in FIGS. 6 and 7, the lithographytechnique and the dry etching technique are used to sequentially processthe second metal film 8 a, the phase-change material 7, the buffer layer6, the third polycrystalline silicon film 5, the second polycrystallinesilicon film 4, the first polycrystalline silicon film 3, and the firstmetal film 2 a into a stripe shape along the first direction. In thismanner, the first metal wiring 2 formed of the first metal film 2 a isformed.

The widths of the second metal film 8 a and the phase-change material 7are similar as those in the second embodiment described above. Further,a similar method as that in the second embodiment described above can beemployed as a method for making the widths of the second metal film 8 aand the phase-change material 7 narrower than other portions. However,the difference from the second embodiment described above is in that thebuffer layer 6 is tapered (tilted). In other words, in the secondembodiment described above, the widths of the buffer layer 6, the thirdpolycrystalline silicon film 5, the second polycrystalline silicon film4, the first polycrystalline silicon film 3 and the first metal wiring 2are the same, while in the third embodiment, the widths of the thirdpolycrystalline silicon film 5, the second polycrystalline silicon film4, the first polycrystalline silicon film 3 and the first metal wiring 2are the same but the width of the upper side of the buffer layer 6 isprocessed to be narrower than the width of the lower side of the bufferlayer 6.

Next, as shown in FIG. 42, the first interlayer film 31 is formed on thesemiconductor substrate 1. A material of the first interlayer film 31 isTEOS for example, and can be formed by a CVD method or the like forexample. The widths of the second metal film 8 a and the phase-changematerial 7 are narrower than the widths of the buffer layer 6, the thirdpolycrystalline silicon film 5, the second polycrystalline silicon film4, the first polycrystalline silicon film 3, and the first metal wiring2. Thus, conditions under which the film is isotropically formed areused to form the first interlayer film 31 so that the first interlayerfilm 31 is filled between the adjacent stacked patterns of the bufferlayer 6, the third polycrystalline silicon film 5, the secondpolycrystalline silicon film 4, the first polycrystalline silicon film 3and the first metal wiring 2, but the sidewall-shaped first interlayerfilm 31 is formed between the adjacent stacked patterns of the secondmetal film 8 a and the phase-change material 7 and a space is formedwithout being filled with the first interlayer film 31.

Further, since the buffer layer 6 is tapered, the space formed betweenthe adjacent stacked patterns of the second metal film 8 a and thephase-change material 7 can be formed deeper than that in the case offorming the first interlayer film 21 in the second embodiment describedabove, for example, down to around the buffer layer 6.

Next, as shown in FIGS. 43, 44 and 45, after the second interlayer film32 is deposited on the semiconductor substrate 1, a CMP technique isused to polish the surface of the second interlayer film 32 to exposethe surface of the second metal film 8 a. A material of the secondinterlayer film 32 is porous MSQ for example, and can be formed by acoating method for example. FIG. 43 is a top view of the memory matrix,where only the second metal film 8 a, the first metal wiring 2 and thesemiconductor substrate 1 are illustrated for facilitating understandingof the structure of the memory matrix. FIG. 44 is a cross-sectional viewof main parts of the memory matrix taken along the line B-B′ of FIG. 43,and FIG. 45 is a cross-sectional view of main parts of the memory matrixtaken along the line A-A′ of FIG. 43.

In the second embodiment described above, the first interlayer film 21has been etched back to adjust the filling depth of the secondinterlayer film 22 before the second interlayer film 22 is formed.Meanwhile, in the third embodiment, since the buffer layer 6 is taperedto adjust the filling depth of the second interlayer film 32 whenforming the first interlayer film 31, the first interlayer film 31 isnot necessary to be etched back unlike in the second embodimentdescribed above. Thus, since the number of manufacturing steps can bereduced, the manufacturing cost can be reduced more than the secondembodiment described above.

Next, as shown in FIG. 46, after a third metal film (same metal film asthe third metal film 9 a used in the first embodiment described above)is formed on the semiconductor substrate 1, the lithography techniqueand the dry etching technique are used to sequentially process the thirdmetal film, the second metal film 8 a, the phase-change material 7, thebuffer layer 6, the third polycrystalline silicon film 5, the secondpolycrystalline silicon film 4, and the first polycrystalline siliconfilm 3 into a stripe shape along the second direction. In this manner,the third metal wiring 9 formed of the third metal film is formed sothat the plug-shaped second metal wiring 8 formed of the second metalfilm 8 a is formed. A material of the third metal wiring 9 is W forexample, and can be formed by a CVD method or the like for example. Atotal film thickness of the second metal wiring 8 and the third metalwiring 9 is preferably 200 nm or less. If the thickness is too large,the processing becomes difficult.

Thereafter, the third interlayer film 33 and the fourth interlayer film34 are formed similarly as those in the manufacturing method describedwith reference to FIGS. 41 to 45 described above. In this manner, thephase-change memory according to the third embodiment shown in FIGS. 38to 40 described above is substantially completed. A filling ratio of thesecond interlayer film 32 or the fourth interlayer film 34 between thememory cells is 25% or less in a plane connecting the center of gravityof the diode DIOD to the center of gravity of the diode DIOD in theadjacent memory cell, and a filling ratio of the second interlayer film32 or the fourth interlayer film 34 between the memory cells is in arange of 50% to 25% in a plane connecting the center of gravity of thephase-change material 7 to the center of gravity of the phase-changematerial 7 in the adjacent memory cell.

A method of operation of the memory matrix and a method of connecting toa peripheral circuit according to the third embodiment are similar asthose in the first embodiment described above. Further, the memorymatrix may be stacked into several layers similarly as in the secondembodiment described above.

As described in the foregoing, according to the third embodiment, theeffects similar as those in the second embodiment described above can beobtained. Further, since the number of manufacturing steps can bereduced as compared with the second embodiment described above, themanufacturing cost can be reduced.

Fourth Embodiment

A memory matrix of a phase-change memory according to a fourthembodiment will be described with reference to FIGS. 47 to 49. FIG. 47is a top view of the memory matrix, FIG. 48 is a cross-sectional view ofmain parts of the memory matrix taken along the line A-A′ of FIG. 47,and FIG. 49 is a cross-sectional view of main parts of the memory matrixtaken along the line B-B′ of FIG. 47. In FIG. 47, only a third metalwiring, a first metal wiring, and a semiconductor substrate areillustrated for facilitating understanding of a structure of the memorymatrix. In the figures, similarly as those in the first embodimentdescribed above, reference numeral 1 denotes a semiconductor substrateand reference numeral 2 denotes a first metal wiring extending along thefirst direction. Reference numeral 3 denotes a first polycrystallinesilicon film, reference numeral 4 denotes a second polycrystallinesilicon film, reference numeral 5 denotes a third polycrystallinesilicon film, and the three layers form a diode DIOD as selectionelement. Further, reference numeral 7 denotes a phase-change material(e.g., Ge₂Sb₂Te₅) as memory element, reference numeral 8 denotes asecond metal wiring (e.g., TiN), and reference numeral 9 denotes a thirdmetal wiring. Furthermore, reference numerals 41 a and 41 b denote abuffer layer (e.g., TiN), reference numeral 42 denotes a firstinterlayer film (e.g., TEOS), reference numeral 43 denotes a secondinterlayer film (e.g., TEOS), reference numeral 44 denotes a thirdinterlayer film (e.g., porous MSQ), and reference numeral 45 denotes afourth interlayer film (e.g., porous MSQ).

In the phase-change memory according to the fourth embodiment, the firstinterlayer film 42 or the second interlayer film 43 is present betweenthe adjacent memory cells at a layer DIL in which the diode DIOD isprovided, and the third interlayer film 44 or the fourth interlayer film45 is present between the adjacent memory cells at a layer PHL in whichthe phase-change material 7 is provided. Therefore, similarly to thesecond embodiment or the third embodiment described above, a thermalconductivity between the memory cells at the layer PHL in which thephase-change material 7 is provided may be set at a different value froma thermal conductivity between the memory cells at the layer DIL inwhich the diode DIOD is provided. For example, when a thermalconductivity of the first interlayer film 42 and the second interlayerfilm 43 is assumed as K_(I5) and a thermal conductivity of the thirdinterlayer film 44 and the fourth interlayer film 45 is assumed asK_(I6), if K_(I6)<K_(I5), it is possible to form a memory cell having astructure in which the diode DIOD is less likely to be at a hightemperature and the phase-change material 7 is likely to at a hightemperature.

Next, a method of manufacturing the phase-change memory according to thefourth embodiment will be described with reference to FIGS. 50 to 56.FIGS. 50, 53 and 55 are top views of the memory matrix, FIG. 51 is across-sectional view of main parts of the memory matrix taken along theline B-B′ of FIG. 50, FIG. 52 is a cross-sectional view of main parts ofthe memory matrix taken along the line A-A′ of FIG. 50, FIG. 54 is across-sectional view of main parts of the memory matrix taken along theline A-A′ of FIG. 53, and FIG. 56 is a cross-sectional view of mainparts of the memory matrix taken along the line A-A′ of FIG. 55.

At first, as shown in FIGS. 50, 51 and 52, the first metal film 2 a, thefirst polycrystalline silicon film 3, the second polycrystalline siliconfilm 4, the third polycrystalline silicon film 5, and the buffer layer41 a are sequentially formed on the semiconductor substrate 1.Subsequently, the lithography technique and the dry etching techniqueare used to sequentially process the buffer layer 41 a, the thirdpolycrystalline silicon film 5, the second polycrystalline silicon film4, the first polycrystalline silicon film 3, and the first metal film 2a into a stripe shape along the first direction. In this manner, thefirst metal wiring 2 formed of the first metal film 2 a is formed.Subsequently, the first interlayer film 42 is formed on thesemiconductor substrate 1. A material of the first interlayer film 42 isTEOS for example, and can be formed by a CVD method or the like forexample. Subsequently, the CMP technique is used to polish the surfaceof the first interlayer film 42 to expose the surface of the bufferlayer 41 a. FIG. 50 is a top view of the memory matrix, where only thefirst interlayer film 42 and the buffer layer 41 a are illustrated forfacilitating understanding of the structure of the memory matrix.

Next, as shown in FIG. 53 and FIG. 54, the lithography technique and thedry etching technique are used along the second direction tosequentially process the buffer layer 41 a, the third polycrystallinesilicon film 5, the second polycrystalline silicon film 4, and the firstpolycrystalline silicon film 3 into a stripe shape. Subsequently, thesecond interlayer film 43 is formed on the semiconductor substrate 1. Amaterial of the second interlayer film 43 is TEOS for example, and canbe formed by a CVD method or the like for example. Subsequently, the CMPtechnique is used to polish the surface of the second interlayer film 43to expose the surface of the buffer layer 41 a. FIG. 53 is a top view,where only the second interlayer film 43, the first interlayer film 42and the buffer layer 41 a are illustrated for facilitating understandingof the structure of the memory matrix.

Next, as shown in FIGS. 55 and 56, the buffer layer 41 b, thephase-change material 7 and the second metal film 8 a are sequentiallyformed on the semiconductor substrate 1. Subsequently, the lithographytechnique and the dry etching technique are used to sequentially processthe second metal film 8 a, the phase-change material 7 and the bufferlayer 41 b into a stripe shape along the first direction. Subsequently,the third interlayer film 44 is formed on the semiconductor substrate 1.A material of the third interlayer film 44 is porous MSQ for example,and can be formed by a coating method or the like for example.Subsequently, the CMP technique is used to polish the surface of thethird interlayer film 44 to expose the surface of the buffer layer 41 b.FIG. 55 is a top view, where only the second metal film 8 a and thethird interlayer film 44 are illustrated for facilitating understandingof the structure of the memory matrix.

Next, a third metal film (same metal film as the third metal film 9 aused in the first embodiment described above) is formed on thesemiconductor substrate 1, and the lithography technique and the dryetching technique are used to sequentially process the third metal film,the second metal film 8 a, the phase-change material 7, and the bufferlayer 41 b along the second direction. Subsequently, the fourthinterlayer film 45 is formed on the semiconductor substrate 1. Amaterial of the fourth interlayer film 45 is porous MSQ for example, andcan be formed by a coating method or the like for example. Subsequently,the CMP technique is used to polish and planarize the surface of thefourth interlayer film 44. In this manner, the phase-change memoryaccording to the fourth embodiment shown in FIGS. 47 to 49 describedabove is substantially completed.

A method of operation of the memory matrix and a method for connectingto a peripheral circuit according to the fourth embodiment are similaras those in the first embodiment described above. Further, the memorymatrix may be stacked into several layers similarly as that in thesecond embodiment described above.

In this manner, according to the fourth embodiment, a thermalconductivity between the memory cells at the layer DIL in which thediode DIOD (stacked pattern of the third polycrystalline silicon film 5,the second polycrystalline silicon film 4, and the first polycrystallinesilicon film 3) is provided may be set at a different value from athermal conductivity between the memory cells at the layer PHL in whichthe phase-change material 7 is provided, thereby facilitating theoptimum design of the phase-change memory having desiredcharacteristics. For example, the first interlayer film 42 or the secondinterlayer film 43 formed of, for example, TEOS is filled at the layerDIL in which the diode DIOD (stacked pattern of the thirdpolycrystalline silicon film 5, the second polycrystalline silicon film4, and the first polycrystalline silicon film 3) is provided, and thethird interlayer film 44 or the fourth interlayer film 45 formed of, forexample, porous MSQ is filled at the layer PHL in which the phase-changematerial 7 is provided. The interlayer film formed of porous MSQ havinga lower thermal conductivity than the interlayer film formed of TEOS isprovided at the layer PHL in which the phase-change material 7 isprovided, thereby reducing the transfer of the heat generated in thephase-change material 7 to the diode DIOD. In this manner, it ispossible to realize a phase-change memory cell in which the diode DIODis less likely to be at a high temperature even when the phase-changematerial 7 becomes a high temperature.

In the foregoing, the invention made by the inventors of the presentinvention has been concretely described based on the embodiments.However, it is needless to say that the present invention is not limitedto the foregoing embodiments and various modifications and alterationscan be made within the scope of the present invention.

For example, also in the case where two or more types of interlayerfilms are formed in the layer in which the phase-change material isprovided and voids are provided according to a combination of the firstand second embodiments described above, similar effects as those in thepresent invention can be obtained.

The present invention can be applied to a nonvolatile memory device inwhich a phase-change material is used as a memory material.

What is claimed is:
 1. A nonvolatile memory device comprising: asemiconductor substrate; a plurality of first metal wirings provided onthe semiconductor substrate and extending along a first direction andbeing electrically connected to a peripheral circuit; a plurality ofthird metal wirings extending along a second direction orthogonal to thefirst direction; memory cells provided at intersections between theplurality of first metal wirings and the plurality of third metalwirings, the memory cells forming an array and including selectionelements provided on the first metal wirings and being electricallyconnected to the first metal wirings; memory elements provided on theselection elements, the memory elements being electrically connected tothe selection elements; and second metal wirings provided on the memoryelements and being electrically connected to the memory elements; thethird metal wirings provided on the second metal wirings and beingelectrically connected to the second metal wirings and peripheralcircuit; and a first interlayer film having a first thermal conductivityand provided on side surfaces of the memory elements and betweenadjacent selection elements and not provided between adjacent memoryelements; and a second interlayer film having a second thermalconductivity provided in a void formed by the first interlayer filmhaving the first thermal conductivity; the second thermal conductivitybeing lower than the first thermal conductivity.
 2. The nonvolatilememory device according to claim 1, wherein the selection elements arediodes and the memory elements are phase-change materials.
 3. Thenonvolatile memory device according to claim 1, wherein the firstinterlayer film having the first thermal conductivity is formed of TEOSand the second interlayer film having the second thermal conductivity isformed of porous MSQ.
 4. The nonvolatile memory device according toclaim 1, wherein a filling ratio of the second interlayer film havingthe second thermal conductivity between the adjacent selection elementsis 25% or less in a plane connecting the center of gravity of theselection element to the center of gravity of the adjacent selectionelement, and a filling ratio of the second interlayer film having thesecond thermal conductivity between the adjacent memory elements is in arange of 50% to 25% in a plane connecting the center of gravity of thememory element to the center of gravity of the adjacent memory element.5. The nonvolatile memory device according to claim 1, wherein a bufferlayer is formed between the selection elements and the memory elements.